1. Field of the Invention
This invention relates to a bladed turbine or impulse wheel for a torque converter of a hydraulic apparatus.
More particularly, the invention relates to a bladed turbine or impulse wheel for a hydraulic torque transmission apparatus for a motor vehicle, of the type which has, substantially, the general form of a half torus, and of the type which comprises, arranged axially and successively in this order, an endless front shell which has the general form of a half torus of large outer diameter, and an endless rear shell coaxial with the front shell and having the general form of a half torus of small outer diameter, between which there is arranged a set of blades, the blades of which extend radially, circumferentially and axially between a concave wall of the front shell and a convex wall of the rear shell in facing relationship therewith.
2. Description of Related Art
There are numerous known examples of bladed wheels which are employed in hydraulic torque converters of the type described above.
In such a converter the bladed wheels constitute either a turbine, that is to say a driven rotor, or an impulse wheel, that is to say a driving rotor, and generally they consist of a circular set of blades which are spaced apart circumferentially at regular angular intervals, a front shell to which the convex edges of these blades are joined, and a rear shell to which the concave edges of the said blades are joined.
The blades are generally formed in a method of fabrication by stamping, and they include spigots for fastening by seaming to the front shell and to the rear shell, which include fastening notches in which the fastening spigots of the blades are introduced before being upset.
The document U.S. Pat. No. 5,109,604 describes such an arrangement.
In that document the convex edges of the blades define a single fastening spigot which extends over the whole length of the blades, while the concave edges of the blades include a single fastening spigot, the fastening spigots of the convex and concave edges of the blades being adapted to be received in the notches of the front shell and rear shell respectively.
It can easily be perceived that such a method of fastening only has a reduced amount of rigidity, which can prove particularly prejudicial to good integrity of the bladed wheel when the fluid pressure between the blades increases. In this connection, an increase in the pressure of the fluid is also accompanied by an increase in vibrations, and in practice, an insufficiently rigid blades mounting increases the deformation of the blades and the danger of disintegration of the elements of the bladed wheel.
In addition, it is known that there prevails in the casing of a motor vehicle hydraulic converter a pressure of 2 to 10 kg/cm.sup.2 while it is working. It is also known that the adoption of a high working pressure enables the influence of cavitation effects to be reduced on the blades of the converter, and that these effects impose a large penalty on the performance of the converter.
However, a conventional arrangement of blades, because it is not rigid enough, does not enable the working pressure of the converter to be increased without running the risk of disintegration of the converter.
Up to the present time, the methods which have to be used for stamping the blades because of the need to give the blades a curved form which is essential in order to establish a plurality of velocity gradients in the fluid in a radial direction of the bladed wheel, have made it necessary to form each blade as a separate piece. This configuration makes it impossible to avoid the use of spigots and notches to assemble the blades in the shells in the manner described above.
Recent improvements in molding methods, particularly as regards the manufacture of components in aluminum alloy or thermoplastic or thermosetting plastics material reinforced with fibers of glass, carbon or Kevlar, now enable complex forms to be made by casting or injection molding with easier stripping from the mould, and in particular they enable components which include a plurality of blades with awkward and complex profiles to be made.